Author Topic: Tektronix 7633 Scope, Can anyone please help Old64goat!!!  (Read 31120 times)

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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #75 on: May 08, 2017, 07:36:54 pm »
Is this the Q1195 pinout Bill was talking about not being able to read the numbers?

 

Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #76 on: May 08, 2017, 08:10:50 pm »
1. The neon bulbs are used as low leakage low capacitance voltage suppressors between the cathode and other tube elements.  This is the first time I have not seen them included on the schematic.  They will often briefly flash when the instrument is turned on or off.

2. The multiplier could be bad but I do not think we would see the symptoms of zero cathode voltage and an intact fuse if that was the case.  Like I posted earlier, I would disconnect the input to the multiplier until the rest of the board works.

3. The flat black discoloration on the left side of the high voltage multiplier is soot attracted by the high positive electrostatic potential and is completely normal.  All CRTs with PDA (post deflection acceleration) accumulate that to some extent.

4. I was very surprised to see that the layout for the high voltage multiplier is included in figure 8-11.  Tektronix refers to it as A9 - Anode Board.  If the multiplier was bad, then I would build a new one from scratch.

5. The pin numbers shown on the schematic at the 2N3055 from top to bottom are 2, 3, 1 for the molded transformer and 5, 1, 2 for the dipped transformer.  So there must have been two different inverter transformers used.

6. My guess is that two of the pins on the primary side are for the +600 volt DC secondary winding and I am sure that the two brown leads coming out of the top are for the CRT heater winding.

7. The +50 volt marking is for diode CR1216.  The winding shown below it is for the +600 volt DC output and also drives the focus and z-axis restorers with AC.

8. That big red capacitor looking thing under the high voltage multiplier is the reed relay.  The glass envelope can be seen at the ends.  My guess is that it is a high voltage vacuum reed relay but I do not remember ever seeing one before.

9. The CRT circuit schematic includes a partial A8 z-axis amplifier and the A9 anode board.  Their are outlines on the schematic separating the different boards.  Usually at the bottom of each outline, it is marked for which board it applies to.  The original drawing has the board outlines highlighted in blue.

10. There is a TO-92 packaged black plastic transistor with a metallic blue flat between the two metal can transistors you counted.  I think Motorola liked to mark their TO-92 transistors that way.

11. Those vertically mounted boards on the high voltage board must be the focus DC restorer and the z-axis DC restorer.

12. The relay coil is marked K1177 and it is shown below and to the right of the inverter transformer on the schematic.  It is left of the RS HORIZ GAIN adjustment.

13. The high voltage multiplier with part number 152-0682-00 has a date code of 8726 so this oscilloscope was produced sometime after the  middle of 1987 making it one of the last ones.  The 7633 was produced from 1974 to 1990.  The 7623B which replaced it was only made in 1991.

14. The plugs all have pin 1 marked with an arrow on the plastic body and usually a marking on the board.

 
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Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #77 on: May 08, 2017, 08:12:45 pm »
Is this the Q1195 pinout Bill was talking about not being able to read the numbers?

Yes.  That is actually the pinout for the connector on the board.  Based on the notation, there were two versions of the inverter transformer and they used a different pinout for the connector going to the transistor.

 
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Offline Cyberdragon

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #78 on: May 08, 2017, 08:28:09 pm »
Do the transistors have little white marks on the bottom of the pins? Those are sockets, the transistors pull out.
*BZZZZZZAAAAAP*
Voltamort strikes again!
Explodingus - someone who frequently causes accidental explosions
 
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Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #79 on: May 08, 2017, 09:30:28 pm »
Do the transistors have little white marks on the bottom of the pins? Those are sockets, the transistors pull out.

I do not know exactly when they changed but late production from Holland did not use the Berg Miniserts found on earlier production.  I have some plug-ins like this and the small signal transistors are soldered into place.

When I am working on these, I remove the transistors and install individual collet pins so the transistor can be replaced without soldering.
 
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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #80 on: May 09, 2017, 01:13:30 am »
Thanks everyone for all your help!!!
 

Offline Martin.M

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #81 on: May 09, 2017, 06:37:18 pm »
if the low voltage PSU is failed, I am pretty shure to have one in the spare parts cabinet

Martin
 

Offline Electro Detective

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #82 on: May 10, 2017, 11:37:41 pm »
Old64goat needs to kick back and take a break   :popcorn:

and listen to some nice music to get pumped   :-+

before going back into the arena   :box:

« Last Edit: May 11, 2017, 10:39:26 am by Electro Detective »
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #83 on: May 11, 2017, 02:23:15 am »
Update from The Old4goat

Thanks everyone for helping!!!
 

Offline BravoV

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #84 on: May 11, 2017, 04:12:30 am »
Not contributing much, but at last video he mentioned there are so many plugs that were unplugged, and need to be plugged correctly. And with that many plugs dangling like that, have to admit they're error prone especially when get distracted.

My tips, use camera, heck, even a crappy cell phone camera will do, as long he can get clear enough picture at close distance as documentation, before unplugging them. I did that every time when tearing down stuffs, or desoldering bunch of interconnect cables.
 
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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #85 on: May 11, 2017, 06:06:02 pm »
From youtube:
Zeebee19712 hours ago (edited)
Diodes CR1202, CR1203  type  VG-12X    http://pdf.datasheet.live/d016da9f/microsemi.com/VG-12X.pdf
"Improved" Tektronix voltage doubler schematic: https://ibb.co/hhSCY5
You can use other transformer secondary lead to connect ac test voltage to the doubler but it is risky without current limiter (very thin secondary coil wire). You can also use signal generator and connect it to the primary side, but you don't have a HV probe (you can control filament voltage only).?
 

Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #86 on: May 11, 2017, 08:33:22 pm »
Diodes CR1202, CR1203 type VG-12X

The high voltage diode selection is not all that critical.  They need to be high voltage, voltage derated, and fast recovery.

Quote
You can use other transformer secondary lead to connect ac test voltage to the doubler but it is risky without current limiter (very thin secondary coil wire). You can also use signal generator and connect it to the primary side, but you don't have a HV probe (you can control filament voltage only).?

I like this idea but it may be perfect for Old4goat in a different form.

Disconnect Q1195 and drive the collector winding with a standard function generator.  Now the input voltage can be carefully controlled and monitored and the output voltages can be measured.  No load will be needed on the CRT winding and no other connections to the board will be needed or are even desired; disconnect everything.

If there is a low voltage problem on the secondary side which seems likely, then it will be possible to track down without using a high voltage probe.

Termination of the function generator's output is not required because of the low frequencies of up to about 40kHz however function generators usually have a 50 ohm series termination limiting them to about 300 milliamps into a short.  This should be enough but if it is not, then a small single ended push-pull amplifier will help drive the inverter transformer to higher outputs.
 
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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #87 on: May 12, 2017, 01:50:02 am »
New update from The Old64goat:


Any help would be greatly appreciated!!!
 

Offline oldway

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #88 on: May 12, 2017, 06:48:49 am »
I have not intervened until now because I have repaired many analogue oscilloscopes of different brands, including Tektronix, but never a 7633.

For me, there are only two possible faults: faulty transformer or faulty voltage doubler.

You worry about things you do not have to worry about: desolder the wire of the voltage doubler that goes to the transformer, whatever the insulation there is on it. You don't have to worry about this insulation !

Power on the scope with the HV board without the voltage doubler and check if you have the - 1475V on the cathode of the tube.

There is no problem to let this auto-oscillator working without load because it is not a flyback and it has a regulation circuit of the -1475V voltage.
 
If you have the correct -1475V voltage, it is the voltage doubler that is defective, if not, it is the transformer that is dead.

Since there are many connectors on this HV board and that there is a risk of error in reassembling the scope, David Hess's proposal is also a good option.

Again, desolder the wire of the voltage doubler that goes to the transformer.

It seems to me that 40Khz is a bit high, I believe that these auto - oscillators work rather at a frequency close to 25 Khz.

Connect the probe (x10 or x100) of your oscilloscope between the ground and the terminal where you have desoldered the voltage doubler wire and feed the transformer primary as you do with 25Khz, but starting from 0V ... (filament of CRT NOT connected !)

Slowly increase the output voltage of your function generator and check the voltage at the secondary with your oscilloscope.

If you have a very low voltage or nothing, the transformer is faulty.

Nb: some scopes as Philips PM3264 have well known issues of corona discharges, but their HV voltage is 17KV's, not 7KV's as this Tektronix 7633.
« Last Edit: May 12, 2017, 07:33:58 am by oldway »
 
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Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #89 on: May 12, 2017, 01:09:54 pm »
For me, there are only two possible faults: faulty transformer or faulty voltage doubler.

These two faults would normally be my first suspicion as well except for the following:

1. There is little or no history of transformer faults in the 76xx series storage oscilloscopes. (1)
2. There is little or no history of high voltage multiplier faults in the 76xx series storage oscilloscopes. (1)
3. If there was a transformer short or a high current short on the secondary side, then the high voltage regulator circuit should drive Q1195 hard enough to blow fuse F814.
4. Nothing was measured on the secondary.  Even with a short, I would have expected something on the secondary side if the primary side was oscillating at all which it apparently was but at a very low level.

Now maybe there are two faults with a shorted transformer or output and damage to the high voltage regulator circuit.  One could have caused the other.

One odd thing I noticed about the 7633 high voltage inverter is that unlike the 465 series high voltage inverter which is practically identical, the 7633 implementation has no primary side over-voltage protection.  I wonder if they did not think it was needed or left it out to save space.  I mention this because if it ran away, then the transformer or secondary side would likely have been damaged.

Quote
It seems to me that 40Khz is a bit high, I believe that these auto - oscillators work rather at a frequency close to 25 Khz.

I could measure the frequency of the high voltage inverter on my 7603 but it uses a different configuration with balanced drive using two 2N3055s.  The 465 series which uses practically the same inverter configuration as the 7623A and 7633 operates at roughly 50kHz.

(1) Maybe there is no such history because the high voltage inverter and multiplier are so difficult to access and diagnose that people give up on it.
 
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Offline oldway

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #90 on: May 12, 2017, 02:14:30 pm »
When you say there is little or no history of faults in the HV transformers or in the voltage doublers of this oscilloscope, you make use of the rules of statistics.

But the statistical rules tell us also that there is more risk of faults in a circuit with high voltage or with high current than in another circuit.

NB: I don't know if Q1195 (TO 2N3055) has been checked for low Hfe ?
A Q1195 with very low Hfe could explain why it is oscilating at very low level without burning the fuse.
« Last Edit: May 12, 2017, 02:40:25 pm by oldway »
 
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Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #91 on: May 12, 2017, 03:40:56 pm »
I have not intervened until now because I have repaired many analogue oscilloscopes of different brands, including Tektronix, but never a 7633.

For me, there are only two possible faults: faulty transformer or faulty voltage doubler.

You worry about things you do not have to worry about: desolder the wire of the voltage doubler that goes to the transformer, whatever the insulation there is on it. You don't have to worry about this insulation !

Power on the scope with the HV board without the voltage doubler and check if you have the - 1475V on the cathode of the tube.

There is no problem to let this auto-oscillator working without load because it is not a flyback and it has a regulation circuit of the -1475V voltage.
 
If you have the correct -1475V voltage, it is the voltage doubler that is defective, if not, it is the transformer that is dead.

Since there are many connectors on this HV board and that there is a risk of error in reassembling the scope, David Hess's proposal is also a good option.

Again, desolder the wire of the voltage doubler that goes to the transformer.

It seems to me that 40Khz is a bit high, I believe that these auto - oscillators work rather at a frequency close to 25 Khz.

Connect the probe (x10 or x100) of your oscilloscope between the ground and the terminal where you have desoldered the voltage doubler wire and feed the transformer primary as you do with 25Khz, but starting from 0V ... (filament of CRT NOT connected !)

Slowly increase the output voltage of your function generator and check the voltage at the secondary with your oscilloscope.

If you have a very low voltage or nothing, the transformer is faulty.

Nb: some scopes as Philips PM3264 have well known issues of corona discharges, but their HV voltage is 17KV's, not 7KV's as this Tektronix 7633.
Thank you Oldway, good to hear from you:)
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #92 on: May 12, 2017, 03:43:58 pm »
Thanks everyone for trying help The Old4goat out!!!
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #93 on: May 12, 2017, 03:58:37 pm »
New update from The Old64goat:
Here is what I found out:
I removed the HV multiplier from the HV transformer and I fed in 100 volts AC 60cly from my varac, I got 60 volts out of the multiplier.

Next I put in 40 KC then lowered it to 25 KC, I had my scope probe on the secondary of the HV transformer where the HV multiplier was connected, NOTHING no signal, I turned up my function generator to max and even set my scope probe to RZ-1, again nothing.

I put my scope probe on pin 3 of the 2N3055 plug and got my signal.

Then I took the resistance readings of the HV transformer, here is what I got:
From the HV transformer terminal where the two HV diodes connect to the reed relay to where the HV multiplier was connected I got 100 ohms.

Next I took a reading from where the HV multiplier was connected on the HV transformer to the terminal where R1217 (10K) is connected and got 163 ohms.

Finally I took a reading from where R1217 (10K) to the HV diodes and got 62 ohms.

I think I got a bad HV multiplier AND a bad HV transformer, replacing the HV board may be the only way but I am not going to dump big money that I do not have into this.
THANKS to all who have helped me on this!!!
 

Offline oldway

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #94 on: May 12, 2017, 04:52:12 pm »
The voltage multiplier seems to be OK, low output voltage is normal because frequency of 60Hz is far too low for normal working.

But HV transformer seems questionable.
 
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Offline Electro Detective

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #95 on: May 12, 2017, 10:16:43 pm »
If it's Game Over, time to put it all back together,
double check all connections,
turn the sucker on,
get verified signals going into it,
play with ALL the controls, tweaking the trigger dial and switches whilst doing so,

then if no life, officially declare it DUT DOA   :-BROKE

If you don't need a cool looker retro doorstop or bookend, then it's Ebay time,

or flog it off here at EEVblog   :-+
« Last Edit: May 12, 2017, 10:19:33 pm by Electro Detective »
 

Offline finom1Topic starter

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #96 on: May 12, 2017, 11:09:03 pm »
New update from The Old64goat:
"Anyway here are the measurements of the HV board without the metal case that has the 2N3055 on it:
6" long, 2" wide and 2" thick.
NOW I found an open transistor on the Z-AXIS board using my SENCORE Cricket but it is too hard for me to see let alone replacing it.
So if one of those guys would be willing to replace that bad transistor on the Z-AXIS booard as well as checking out the HV board I will give the dementions of the Z=AXIS board:
6" long, 2" wide and 3/4" thick.
I only tested two transistors on the Z-AXIS board so there may be more bad transistors.
As I understand that board is part of the CRT circuit.
Bill"
 

Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #97 on: May 12, 2017, 11:20:10 pm »
I am not convinced the high voltage transformer is bad but I can understand not wanting to mess with it anymore.  There are other tests I would do for confirmation and it is not clear to me exactly how Old64goat tested it.

To me this seems like an ideal 7633 to repair for someone who is familiar with them.  Whatever is going wrong with the high voltage board is probably the only problem.
 
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Offline David Hess

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #98 on: May 13, 2017, 04:18:21 am »
I did a little research on replacement parts.

There *is* a history of 7633 transformer failures although probably no more than any other 7600 series oscilloscope.  My guess is that most diagnosis never get that far because of difficult access to the high voltage board.  The 7623A used the same transformers.

Replacement transformers are non-existent.  Replacement high voltage boards are expensive.  However you can probably get a 7623A (1) or 7633 with a known working high voltage board which has the transformer for $40 or less on Ebay; unfortunately shipping will be like $60.  Maybe a cheap 7623A or 7633 can be found on Craigslist to save on shipping charges.

Q1184   151-0126-00   2N2484   NPN High Gain Amplifier
Ideal replacements: 2N5088/9 BC546/48/50
Would probably work: 2N3904
Q1187   151-0188-00   2N3906   PNP General Purpose Amplifier
Ideal Replacements: 2N3906
Would probably work: 2N4403 2N2907
Q1190   151-0136-00   2N3053   Medium Power Amplifier
Ideal Replacements: MJE180/1/2
Would probably work: 2N4401 2N2222 (2)
Q1195   151-0140-00   2N3055   Power Transistor 0.3MHz
Ideal Replacements: 2N3055 (0.3MHz) 2N3771G 2N3772G
Would probably work: 2N3055AG MJ15015

(1) I found suitable 7632As which went for $10 and $25 recently on Ebay and they also included some plug-ins.  The shipping cost for each was about $60 though.

(2) For extra derating, I might use a pair of Vbe matched 2N4401s in parallel if I did not have a suitable TO-126 or TO-225 packaged transistor.  There are higher power TO-92 transistors but they are more expensive than the recommended MJE180 series.
« Last Edit: May 13, 2017, 08:54:54 am by David Hess »
 
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Offline oldway

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Re: Tektronix 7633 Scope, Can anyone please help Old64goat!!!
« Reply #99 on: May 13, 2017, 06:52:26 am »
I am also not sure that the transformer is defective, it would be necessary to make additional tests.

The current with a 600R function generator is very low, perhaps insufficient.

50R was already much better.

Ideally, the primary of the transformer should be supplied from a LF amp with a 4.7R series resistor.

Magnetizing current and transformer ratio would be compared with values of a known good working transformer of the same type....but this is not available....

Repairing without spare parts is something very difficult.... |O
 
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